Vapour turbines which operate with geothermal vapours come into contact with aggressive and/or corrosive substances for the components of the turbine itself.
Even small quantities of aggressive substances such as chlorides and sulfides, cause the corrosion of the vapour turbine components, such as rotor blades, stator blades and sealing laminas.
The materials currently used for vapour turbine components are martensitic stainless steels which are strongly subject to corrosion phenomena on the part of aggressive and/or corrosive agents.
The corrosion is particularly high in the transition area between overheated vapour and damp vapour (Dew Point).
In this area, the solid particles contained in the geothermal vapour form large deposits on the surface of the blades.
During the functioning of the turbine, the deposits accelerate the corrosion process under way, due to the increase in localized concentration of corrosive agents such as chlorides and sulfides.
Corrosion of the turbine components jeopardizes the correct functionality of the turbine itself as well as the preventive maintenance plan programmed for it.
In order to reduce maintenance interventions and consequently also substitution of the components themselves, the geothermal vapours containing aggressive substances in a higher quantity than a predetermined percentage, are “washed” with water.
This reduces the concentration of aggressive substances present in the geothermal vapours.
A first disadvantage is that the washing operations of geothermal vapours causes an increase in the running and maintenance costs of the plant, also increasing its complexity.
Another disadvantage is that upon washing the vapour, the enthalpy available at the turbine inlet is reduced and consequently the useful work of the turbine itself is reduced.